An exhaust gas purification system for an internal combustion engine using a three-way catalyst can not sufficiently oxidize hydrocarbons (HC) discharged during cold engine operation conditions due to the fact that the catalyst has not reached an activation temperature.
JP09-085049 published by the Japanese Patent Office in 1998 discloses an HC trap added to an exhaust gas purification system. The HC rap has the function of temporarily trapping HC in exhaust gas from the internal combustion engine. The trapped HC is discharged as the temperature increases. The exhaust gas purification system according to his prior art disposes the HC rap upstream of the three-way catalyst.
When the exhaust gas from the engine has a low temperature, the HC rap in this system traps HC Thereafter when the three-way catalyst has reached an activation temperature, the HC trap releases the trapped HC and the three-way catalyst oxidizes and converts HC released from the HC trap into carbon dioxide (CO2) or steam (H2O).